The present invention relates to a radio receiver and a method for identifying spreading codes. The present invention particularly relates to a radio receiver and a method for identifying spreading codes in movable body radio communication employing the Code Division Multiple Access (hereinafter referred to as xe2x80x9cCDMAxe2x80x9d) system.
Synchronous systems between base stations and asynchronous systems between base stations are applicable in movable body radio communication systems employing the CDMA system. However, it is necessary for the synchronous systems between base stations to use another system such as the Global Positioning System (GPS). Consequently, the asynchronous systems between base stations that are simpler and easier than the synchronous systems are frequently used in the mobile radio communication systems.
In a conventional CDMA asynchronous cellular system between base stations, each base station holds an intrinsic long period spreading code (hereinafter referred to as xe2x80x9clong codexe2x80x9d) for identification, and a mobile station identifies the long code of a cell in which the mobile station connects a link by performing a cell search at the time of its initial connection and handover.
Hereinafter, FIG. 1 is referred while a conventional radio receiver and its identification method of the long code is described. FIG. 1 is a block diagram showing the schematic configuration of the conventional radio receiver. Incidentally, it is supposed that a radio signal is constituted of a plurality of frames and each frame is constituted of a plurality of slots.
In FIG. 1, an antenna 1 receives radio signals, and a radio signal reception section 2 performs the reception processing of the received signals. A slot/chip synchronization section 3 detects the timing when correlation values take the maximum value by shifting each slot of the received signals at every chip while multiplying each slot by a known short period spreading code (hereinafter referred to as xe2x80x9cshort codexe2x80x9d) for realizing slot synchronization and chip synchronization at the same time.
A plurality of correlation sections 4 calculate correlation values by multiplying the received signals by spreading codes input from a switch 8, which will be described later, respectively. A correlation section 5 receives identified long codes from the switch 8 and performs the despreading processing of the received signals.
A maximum correlation value detection section 6 detects the maximum correlation value among the plural correlation values calculated by the plural correlation sections 4. When the number of the long codes held by a spreading code generation section 7, which will be described later, namely the number of the long codes the correlation values of which with the received signals should be calculated, is larger than the number of the correlation sections 4, the maximum correlation value detection section 6 temporarily stores the calculated correlation values and detects the maximum correlation value after all correlation values have been calculated.
The spreading code generation section 7 stores a plurality of long codes, and outputs the stored long codes to the switch 8 under the control of a spreading code setting section 9, which will be described later. The switch 8 switches the long codes output from the spreading code generation section 7 to output them to any of the plural correlation sections 4 or the correlation section 5 under the control of the spreading code setting section 9, which will be described later.
The spreading code setting section 9 controls the spreading code generation section 7 and the switch 8 so that the correlation values of all of the long codes with the received signals can be calculated. The spreading code setting section 9 identifies a long code, which is judged by the maximum correlation value detection section 6 to be the long code generating the maximum correlation value, as the long code of the cell in which a link is connected, and sets the long code in the correlation section 5. A demodulation section 10 obtains received data by performing the RAKE combining processing of the received signals, the error correction processing of them, or the like after receiving the despreading processing by the correlation section 5.
As described above, the conventional radio receiver calculates the correlation values of all of the long codes with the received signals, and identifies a long code generating the maximum correlation value as the long code of the cell in which a link is connected. The conventional radio receiver then performs the despreading processing of the received signals by the use of the identified long code to begin communication.
However, the conventional radio receiver has a problem that, because the number of the long codes is determined to be a fixed number in accordance with the design of its system, if the number of the correlation sections is increased, the scale of the equipment becomes large in spite of the decrease of the time necessary for the identification of the long codes, and if the number of the correlation sections is decreased, the time necessary for the identification of the long codes is elongated in spite of the decrease of the scale of the equipment.
The object of the present invention is to provide a radio receiver in which the scale of the configuration for the calculation of the correlation values is suppressed to be the minimum scale, and in which the time necessary for the identification of its long codes is shortened.
The subject matter of the present invention is to identify a long code by dividing a long code group including the prospective long code to be identified into a plurality of groups, and by selecting a group having the maximum correlation value in the results of the addition of the long codes in each group as the group including the long code to be identified, and further by repeating the grouping and the narrowing down of the groups in a radio receiver.